Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
  • C09K8/02—Well-drilling compositions
  • C09K8/04—Aqueous well-drilling compositions
  • C09K8/14—Clay-containing compositions
  • C09K8/18—Clay-containing compositions characterised by the organic compounds
  • C09K8/22—Synthetic organic compounds
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S507/00—Earth boring, well treating, and oil field chemistry
  • Y10S507/925—Completion or workover fluid

Definitions

• This invention relates to a drilling and completion fluid and a method of preparing the same.
• Drilling mud or drilling fluid is a more-or-less complex mixture of chemicals used in drilling of a well to perform a variety of functions.
• Drilling mud comprises a liquid or slurry that is pumped down the drill string to exit through nozzles in the bit immediately adjacent the formation being penetrated.
• the drilling mud flows upwardly in the annulus between the drill string and the wall of the hole to the surface and provides a variety of functions.
• the drilling mud cools and lubricates the bit, delivers hydraulic horsepower to the bit, carries cuttings upwardly in the hole during circulation, suspends the cuttings in the bore hole when circulation stops, prevents blowouts, minimizes water loss into permeable formations, lubricates between the drill string and the bore hole wall and performs assorted other functions.
• drilling muds There are all sorts of drilling muds. The most elementary drilling mud is water mixed with drilled solids and is often called "native" drilling mud. Some of the drilled solids are clays which, when finely ground, provide several of the functions of drilling mud. Some of the drilled solids add weight to the slurry which raises the density of the mud to 9.2-9.9 lbs/U.S. gallon which is sufficient to control normal pressures at shallow depths in many actively drilled areas.
• Native mud was the earliest used in the rotary drilling of oil and gas wells. It was soon discovered that native drilling mud provides almost no control over the loss of water into permeable formations, tends to wash out or enlarge the diameter of the hole, accumulate shale balls on the bit and have other major disadvantages. Since that time, a wide variety of chemicals have been added to drilling mud to overcome real or perceived problems with native drilling mud.
• One desirable characteristic of a drilling mud is that it sets up or gels, like Jello, as it sits quietly. This characteristic is desirable so that cuttings or weight material in the drilling mud don't fall by gravity through the drilling mud toward the bottom of the hole when circulation stops. This characteristic is imparted to drilling mud by a gelling agent, such as drilled solids, bentonite and/or subbentonitic clays or mixtures thereof.
• a drilling mud creates a filter cake of low permeability on the face of permeable formations.
• the filter cake should be relatively thin and hard as opposed to thick and gooey.
• the filter cake is created because the pressure in the borehole exceeds the pressure in a permeable formation penetrated thereby and liquid from the mud is moved into the permeable formation, leaving on the face of the formation a filter cake comprising the solids entrained in the mud.
• the liquid lost to the formation is called filtrate.
• filtrate When a large amount of filtrate passes across the formation face, a thick filter cake is deposited.
• a small amount of filtrate passes across the formation face, a thin filter cake is deposited.
• One function of the filter cake is to limit additional filtrate loss into the formation after the filter cake is created.
• a wide variety of chemicals have been used to produce thin filter cakes or reduce filtrate loss, such as carboxymethyl cellulose, lignite, lignosulfonates, Resin-X- available from Magobar, Miltemp - a high temperature polymer available from Milpark, Claytemp - a polymer available from Barclays, Soltex - an asphalt based material available from Drilling Specialty and the like.
• One purpose of the good filter cake is to reduce the quantity of filtrate lost to a permeable formation which is desirable for two reasons.
• a fresh water filtrate for example, causes many clays such as montmorillonite and ilite to swell.
• Sodium hydroxide is added to many drilling muds to raise the pH thereof substantially because it was learned years ago that an alkaline drilling mud does not swell clays as contrasted to a neutral or acidic drilling mud.
• most pre-existing muds to which the additives of this invention are used are quite alkaline because sodium hydroxide has usually been added thereto.
• the use of sodium hydroxide is typically suspended because the glycerines used are sufficiently alkaline to keep the pH high.
• a completion fluid is a liquid material used during the completion phase of a well, i.e. while perforating a productive formation or conducting operations on a well after it has been drilled and cased but excluding formation fracturing operations.
• a completion fluid differs from a drilling fluid mainly because it does not have to carry large quantities of cuttings upwardly in the annulus of the well bore, the only cuttings produced during completion operations being relatively small quantities of cement, cast iron and rubber, as may occur when drilling up DV tools, bridge plugs, squeeze jobs or the like.
• completion fluids do not normally contain a gelling agent unless the fluid is very heavy and weighted with a solid weighting agent.
• There is not as much a requirement for lubrication in a completion fluid because there is considerably less friction between the inside of oilfield casing and a work string than between the bore hole wall and a drill string.
• completion fluids must have properties similar to drilling muds, i.e. they must be non-damaging to potentially productive formations, they must be sufficiently heavy to offset the bottomhole pressure of permeable formations and the like.
• the fluid of this invention is eminently suitable as a completion fluid because it does not swell clays which may be present in productive formations, it is capable of withstanding significantly high bottom hole temperatures without degradation, its flow characteristics are not degraded by the introduction of solid, liquid or gaseous contaminants, it can be weighted to any reasonable density for pressure control and it is rather inexpensive.
• a completion fluid made in accordance with this invention is quite suitable for use behind a packer to provide a non-corrosive relatively heavy liquid.
• Another object of this invention is to provide an improved completion fluid which is particularly non-damaging to common clays found in permeable formations potentially productive of hydrocarbons.
• the present invention provides a fluid comprising a mixture of solids and liquids, the solids comprising a gelling agent selected from the group consisting of drilled solids, bentonite, subbentonitic clays, and mixtures thereof, the liquids comprising a solution of water, a glycerine selected from the group consisting of glycerine, polyglycerine and mixtures thereof and a glycol selected from the group consisting of alkylene glycol, polyalkylene glycol, and mixtures thereof, the glycerine and glycol comprising not more than 20% by volume of the liquid, the volume of the glycol being 2-50% of the volume of the glycerine and glycol.
• a gelling agent selected from the group consisting of drilled solids, bentonite, subbentonitic clays, and mixtures thereof
• the liquids comprising a solution of water, a glycerine selected from the group consisting of glycerine, polyglycerine and mixtures thereof and
• a fluid for use in petroleum wells comprising water and at least 6% by volume of a water soluble liquid selected by the group consisting of a polyglycerine and mixture of a polyglycerine with glycerine.
• a water based drilling mud may comprise water, a gelling agent, a defoamer and at least 6% by volume of a water soluble glycerine taken from the group consisting of glycerine, polyglycerine and mixtures thereof.
• a filter loss enhancer may be added.
• a weight material may be added.
• U.S.-A- 2191312 discloses a drilling fluid intended to prevent the disintegration of a heaving shale which is defined as one which, in contact with the ordinary drilling mud, swells or disintegrates spontaneously so much as to interfere with the drilling operation.
• the drilling fluid comprises a suspension of clay in a mixture of water and at least 20% by weight of glycerol, and preferably more than 40% by volume of glycerol.
• Cannon discloses only the use of glycerol, i.e. simple glycerine and in an amount of at least 20% by weight of the mud and preferably 40% or more.
• One aspect of the present invention excludes the use of glycerol and requires the fluid to include a polyglyceride or a mixture of a polyglyceride with glycerine with a lower limit of 6% by volume.
• polyglycerols e.g. diglycerol, triglycerol and others are quite superior to simple glycerol in inhibiting shale hydration, dispersion or disintegration.
• the polyglycerols in the fluids can be used at a much lesser concentration to achieve the same degree of shale disintegration obtained with glycerol alone, or to obtain a quite improved degree of inhibition of shale disintegration when used at the same concentration as the glycerol used in the drilling fluid disclosed by Cannon.
• Natural glycerine and Dow W-80 were formulated as follows:
• Enough base mud was made up to conduct all of the tests from one batch of mud. This reduces variation between batches of mud and their effect on interpretation of data.
• the base mud was kept under refrigeration at 4° C to prevent hydrolysis of organic constituents and decomposition due to bacterial activity until ready for use.
• the residue was sieved from the 10 mesh screen and put on a tared drying dish where the sample was taken to complete drying at 105° C, cooled and weighed. The residue was then calculated to provide a percent recovery value.
• Bentonite used in oil field mud is a fine powder and is added to ordinary drilling mud by simply pouring it out of a sack into a hopper emptying into a conduit through which mud is flowing.
• the bentonite particles hydrate and swell by adsorption of water contained in the drilling mud.
• Dry powdered bentonite added to a mud system of this invention is not water wet and accumulates in clay clumps floating on top of the mud.
• the bentonite is accordingly not wet by the water in the drilling mud.
• bentonite is prehydrated, i.e. it is mixed with water in a separate tank to form a slurry which is then introduced into the fluid of this invention.
• Drilling the same materials with a mud of this invention has little or no perceivable affect on the drilling mud.
• a simple experiment illustrates the peculiar result. About 500 ml of a mixture is prepared in a beaker, the mixture containing about 40% water and 60% by volume of a glycerine-glycol solution. A small quantity of salt less than enough to supersaturate the solution is poured into the beaker and the beaker shaken well. Within a minute or two, salt particles can be seen settling out in the bottom of the beaker. Little or no salt enters the solution even though the liquid phase is 40% water. Thus, salt cannot contaminate the solution and salt particles are merely suspended like a non-soluble material.
• the filtrate does not swell clays such as montmorillonite, ilite or the like when the proportion of glycerines is sufficiently high.
• the filtrate produced in a standard API filter press is a solution of water, glycerine and defoamer in the same proportions as in the drilling mud.
• a montmorillonite tablet dropped into a beaker of the filtrate where the glycerine concentration is above about 25-30% by volume shows no perceptible swelling of the tablet in two days.
• a montmorillonite tablet added to fresh water swells and disintegrates in a minute or two.
• swelling of a montmorillonite tablet is slowed significantly.
• swelling of montmorillonite tablets is progressively reduced.
• Drilling of a typical well begins by using a so called “spud” mud.
• spud mud is prepared by pumping highly treated mud from a previous well into a vacuum truck and watering it down with sufficient water to make it thin.
• spud mud is prepared by mixing bentonite in water so the resultant suspension contains 25-30 lbs of bentonite per barrel of water.
• the surface shoe and cement are drilled, followed by drilling out under surface.
• the additives of this invention are admixed with the pre-existing mud. It may be that there is sufficient gelling agent, i.e. drilled solids, bentonite, subbentonitic clays, and mixtures thereof, in the mud. In this event, a solution of glycerine and defoamer is simply added to the mud.
• a slurry of bentonite and water may be prepared in a slug tank and slowly added to the mud tank or pit to increase the quantity of gel in the mud after adding glycerine and defoamer to the mud.
• a slurry of bentonite and water may be prepared in a slug tank and slowly added to the mud tank or pit while contemporaneously adding a solution of glycerine and defoamer to the mud.
• dry powdered bentonite cannot be added to a mud system containing adequate quantities of glycerine and defoamer because the bentonite is not wet by the liquid phase.
• the volume of a mud system is the sum of the volume of the hole and the volume of the mud tanks or pits.
• the volume of a mud tank or pit is usually assumed to be constant even though they partially fill up with drilled solids during the course of drilling a well.
• the volume of the hole increases substantially with drilling because the hole gets deeper.
• the volume of mud in a mud system has to increase during the course of drilling a well or the mud tank or pit will run dry. Accordingly, liquid is more-or-less continuously added to a mud system. In an ordinary water based drilling mud, liquid is added by allowing a stream of water from a water hose to flow into the mud return line or across the shale shaker.
• water is added conventionally but the liquid additives are prepared and placed in a tank of adequate size, e.g. a frac tank, and periodically pumped into the mud tank.
• a tank of adequate size e.g. a frac tank
• the mud engineer clocks the time necessary to fill a five gallon bucket from the pump. If the analysis of the mud and the increase in hole volume will necessitate the daily addition of some volume of the glycerine-defoamer solution.
• the mud engineer determines this needed volume addition and leaves instructions for each driller to operate the compressed air driven pump for a predetermined number of minutes each tour, thereby adding the necessary volume of glycerine-defoamer solution every eight hours or so.
• a mud engineer conducts a variety of analyses on the drilling mud at frequent intervals, at least once a day. In the course of these tests, it is often determined that the sampled mud is deficient in one or more respects and appropriate corrective action is taken.
• mud system of this invention there are usually only five things to do: (1) control the amount of gelling agent to be sure there is enough to carry drilled solids to the surface and provide sufficient gel strength to suspend solids if circulation is stopped; (2) control the filter loss of the mud by adding a filter loss reducer; (3) control the amount of glycerine-defoamer solution; (4) maintain the desired mud weight by adding weight material if necessary and (5) keep the amount of solids suspended in the system under control by using mud cleaning equipment such as a mud centrifuge, cyclone or the like.
• mud cleaning equipment such as a mud centrifuge, cyclone or the like.
• the desired amount of gelling agent in the mud varies substantially for a variety of reasons including the type gelling agent used.
• High yield Wyoming bentonite which is a sodium montmorillonite, is the preferred gelling agent in modern drilling muds and is preferred with the mud of this invention.
• Other types of clays are quite suitable, such as medium yield drilling clays, calcium montmorillonite clays, and drilled solids.
• the amount of gelling agent to be used may range from about 5% by weight of the mud up to as high as about 75% by weight.
• the amount of bentonite in a drilling mud is determined either by a measurement of the gel strength of the mud or by a test known in the art as an MBT test. If there is too much bentonite, liquid is added to the mud system until the bentonite is diluted to the desired concentration. If there is too little bentonite, bentonite is added in a slurry form as previously mentioned.
• a filter loss reducer may be added to the mud.
• the preferred filtrate loss reducer of this invention is powdered lignite, a conventional material for this purpose. Powdered lignite is added by mixing with water in a slug tank and then adding the slurry to the mud tank because the powdered lignite is not readily admixed with a drilling mud containing the glycerine-defoamer solution of this invention.
• the glycerine or glycerol to be used may be simple glycerine, diglycerine, triglycerine, tetraglycerine, pentaglycerine, heavier polyglycerines and mixtures thereof.
• a preferred glycerine is a mixture of glycerine and polyglycerines available from Dow Chemical Company, Freeport, Texas and is known as Polyglycerine W-80.
• This material is a hydroxyl functional liquid which consists of various glycerols in an aqueous solution having the following typical properties:
• Polyglycerine W-80 available from Dow Chemical is a byproduct of some chemical manufacturing operation of which applicant is unaware. Thus, it would seem that the available material would vary from batch to batch, although no noticeable differences have been perceived in using this material in several wells. It is believed that Polyglycerine W-80 is an azeotropic mixture of water and glycerines because heating this mixture causes the mixture to boil off at a constant temperature and creates a reduction in the volume of material but does not apparently change the composition of the remaining material.
• the glycerine in the drilling mud of this invention has a plurality of functions. It acts to lubricate the contacting surfaces between the drill pipe and the bore hole wall, to reduce filtrate in standard API mud filtrate tests with a filter press, to control the flow properties of the mud by lowering the yield point of the drilling mud and the plastic viscosity and to minimize sloughing shale problems.
• a major function of the glycerine is to get the water in the mud in solution and affect it in such a manner that drilled contaminates like salt, gypsum, anhydrite and calcium carbonate are held in suspension rather than in solution thereby preventing deterioration of the mud.
• the exact mechanism is not yet understood, but it is clear that the mud of this invention does not wet ordinary drilled solids and thus does not swell clays of the type typically encountered in drilling a well.
• a drilling mud of this invention includes at least 6% by volume glycerine.
• the proportion of glycerine increases to about 25-30% by volume, the rate of hydration of montmorillonite tablets decreases until substantially no swelling is perceptible. It is accordingly preferred that the proportion of glycerine exceed 25%.
• a defoamer of any suitable type is used in an amount effective to eliminate foaming or reduce it to unobjectionable levels.
• the preferred defoamer used in the drilling mud of this invention is a glycol selected from the group consisting of an alkylene glycol such as ethylene glycol, propylene glycol, and the like, a polyalkylene glycol such as polyethylene glycol, polypropylene glycol and the like and mixtures thereof. It appears that polypropylene glycol is the preferred glycol because it is less sensitive to high temperatures found in many moderate to deep wells. In most wells of moderate temperature, it appears that any glycol will act satisfactorily.
• defoamers are also usable in the fluid system of this invention such as LD-8 - an alcohol based defoamer available from Milpark, aluminium stearate and diesel, methyl ethyl ketone, methanol, Barclay's defoamer, CamServ defoamer, Unibar defoamer and Bosco defoamer.
• LD-8 an alcohol based defoamer available from Milpark, aluminium stearate and diesel, methyl ethyl ketone, methanol, Barclay's defoamer, CamServ defoamer, Unibar defoamer and Bosco defoamer.
• glycol is a preferred defoamer because it has a variety of other desirable attributes. It not only acts as a foam breaker or reducer to keep the glycerine from foaming excessively but also assists in controlling the flow properties of the fluid and reduces API filtrate loss.
• Sufficient glycol is used to eliminate foaming or reduce it to an unobjectionable level.
• a greater quantity of glycol may be used to take advantage of some of its other advantageous properties if such are wanted.
• the amount of glycol is typically proportional to the amount of glycerine and varies between 2-50% by volume of the glycerine and is a minor component when compared to the amount of glycerine in the system.
• the fluid includes solids in the form of a gelling agent selected from the group consisting of drilled solids, bentonite, subbentonitic clays and mixtures thereof and also a glycol
• a gelling agent selected from the group consisting of drilled solids, bentonite, subbentonitic clays and mixtures thereof and also a glycol
• simple glycerine can be used, the glycerine and glycol comprising not more than 20% by volume of the liquid and the volume of the glycol being 2-50% of the volume of the glycerine and glycol.
• a well in Plaquemines Parish, Louisiana is drilled to 9200 feet using a conventional brackish water-caustic-bentonite-chrome lignosulfonate mud.
• enough liquid glycerine-glycol solution is added to constitute 10% by volume glycerine-glycol solution.
• the amount of glycol in the additive is 10%.
• the glycerine component is Polyglycerine W-80 from Dow Chemical.
• the amount of glycerine in the drilling mud is about .10 x .90 x .75 or about 6.6% by volume.
• the mud properties at 12,078 feet were: weight - 11.5 #/gal funnel viscosity - 46 seconds plastic viscosity - 15 cP yield point - 9 cP gel strength - 2/6 API filtrate - 5.6 cc cake thickness 2/32 inches solids content - 23% chlorides - 19,000 ppm pH - 10.5
• Drilling and logging progressed normally without difficulty.
• a well in LaFource Parish, Luisiana is drilled to 8000 feet using a conventional fresh water-caustic-bentonite-lignite-chrome lignosulfonate mud.
• the well is sidetracked and 140 barrels of glycerine-glycol solution is added to the mud system, having a total volume of 1190 barrels.
• the amount of glycol in the additive is 10%.
• the glycerine component is Polyglycerine W-80 from Dow Chemical.
• the amount of glycerine in the drilling mud is about 145/1190 x .9 x .75 or about 8.2% by volume.
• the mud properties at 8246 feet were: weight - 9.6 #/gal funnel viscosity - 37 seconds plastic viscosity - 11 cP yield point - 7 cP gel strength - 3/7 API filtrate - 3.4 cc cake thickness 2/32 inches solids content - 5% chlorides - 2800 ppm pH - 10.0
• glycerine-glycol solution Twenty to thirty barrels of glycerine-glycol solution is added daily to the mud system to maintain the glycerine concentration. In addition, bentonite and lignite are added daily. Periodically, barite is added for weight. At 10,330 feet hole angle is 43 °. Except for rig breakdowns, drilling proceeds normally to total depth. During one rig breakdown, the drill string is in the open hole and not moved for two hours. After the breakdown is corrected, the driller raises the travelling block and, after pulling 15,000 pounds in excess of the weight of the drill string, the drill string comes loose. It was considered a minor miracle that the drill string wasn't stuck and attributed to the lubricity of the drilling mud of this invention.
• a native drilling mud is conditioned by adding thereto a prehydrated bentonite-lignite-slurry and a solution of glycerine and methanol sufficient to constitute 35% glycerine-methanol by volume.
• the glycerine is simple glycerol.
• the methanol constitutes 10% by volume of the glycerine-methanol solution.
• a montmorillonite tablet is added to filtrate collected from an API filter press. No swelling of the tablet is noted.
• a spud mud is prepared with fresh water by mixing 30# of bentonite per barrel of mud. To this mixture is added a quantity of glycerine mixture sufficient to amount to about 20% by volume of the mud system.
• the glycerine mixture consists of 50% simple glycerol and 50% diglycerine along with enough Barclay's defoamer to prevent foaming.
• a montmorrillonite table is added to filtrate collected from an API filter press. No swelling of the tablet is noted.
• a drilling mud is prepared by adding to a native mud-bentonite-caustic drilling mud enough liquid glycerine-glycol additive to constitute 55% by volume glycerine-glycol.
• the glycerine is a mixture of 1/3 glycerine, 1/3 diglycerine and 1/3 triglycerine.
• the glycol is 10% of the glycerine-glycol additive.
• a montmorrillonite tablet is added to filtrate collected from an API filter press. No swelling of the tablet is noted.
• a drilling mud is prepared by adding to a native mud-bentonite-caustic-lignite-chrome lignosulfonate slurry enough liquid glycerine-defoamer additive to constitute 35% by volume of the mud.
• the defoamer is Barclay's defoamer and constitutes 5% by volume of the additive.
• a montmorillonite tablet is added to filtrate collected from an API filter press. No perceptible swelling of the tablet is noted.
• a drilling mud is prepared by adding to a native mud-bentonite-caustic-lignite-chrome lignosulfonate slurry enough simple glycerine to amount to 75% by volume of the mud.
• a methanol defoamer is added, amounting to 5% by volume of the mud.
• a montmorillonite tablet is added to filtrate collected from an API filter press. No swelling of the tablet is noted.
• a 10 #/gal completion fluid is desired.
• Polyglycerine W-80, weighing 10.7 #/gal is diluted with enough polypropylene glycol to produce a 10 #/gal mixture. No bentonite or barite is used.
• a 15 #/gal completion fluid is desired.
• Polyglycerine W-80, weighing 10.7 #/gal, is diluted with enough water to produce a 10 #/gal mixture.
• 5% by volume methanol is added to control foaming.
• a bentonite-water slurry is added to provide 10# of bentonite per barrel of completion fluid.
• Enough barite is added to raise the density to 15 #/gallon.
• a 9.5 #/gal completion fluid is desired.
• a 50-50 mixture of simple glycerine and diglycerine is diluted with enough water to weigh 9.5 #/gal.
• Barclay's defoamer in an amount of about 3% by volume. No barite or bentonite is used.
• a 10 #/gal completion fluid is desired.
• Simple glycerine and polypropylene glycol are mixed in a ratio of 6:1. This solution is diluted with water to weigh 10 #/gal.

Landscapes

• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Bulkheads Adapted To Foundation Construction (AREA)
• Lubricants (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=21984491

Family Applications (1)

Country Status (5)

Cited By (3)

Families Citing this family (50)

Family Cites Families (16)

• 1987
  • 1987-05-26 US US07/053,472 patent/US4780220A/en not_active Expired - Lifetime
• 1988
  • 1988-04-28 CA CA000565412A patent/CA1296514C/en not_active Expired - Fee Related
  • 1988-05-19 MX MX011557A patent/MX170158B/es unknown
  • 1988-05-25 DE DE3852572T patent/DE3852572D1/de not_active Expired - Lifetime
  • 1988-05-25 EP EP88304749A patent/EP0293191B1/de not_active Expired - Lifetime

Also Published As

Similar Documents

Legal Events